Get info of the selected record in AttachAction

I have a very simple AttachAction in a RelationManager. The user selects whatever option they want, using this

$action->getRecordSelect(),

In that very moment, from that selection, I need to populate a couple fields below.

I know how to get the ownerRecord, I now how to get the data that will be saved, and those are not my questions. I need whatever information I can from that selection. Any ideas?
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